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Late fuel injection directly into the cylinder of a 2-stroke engine is desirable to prevent escape of some fuel into exhaust system during cylinder scavenging. This leaves little time for fuel evaporation and mixture preparation and puts a premium on the degree of fuel atomization needed during the injection process. Although a respectable degree of atomization can be attained in fuel systems with high pressure, liquid-only injection, further improvements can be made when compressed air is used to assist atomization. A novel air-forced (AFI) fuel injection system for in-cylinder injection in a 2-stroke engine is described. The system employs compressed air to force a metered quantity of fuel from the fuel injector internal cavity past a spring loaded poppet valve. A fog-like cloud containing a rich mixture of fuel and air is injected into the cylinder. As a result, an exceptionally fine atomization is achieved.

Usage of solenoid valves capable of controlling fuel delivery to several engine cylinders in succession reduces the cost and complexity of electromagnetic fuel injection systems. A new type of injection pump employing solenoid valves with shuttles is described. In a multiplunger pump such a solenoid valve controls operation of two plungers in succession. The number of required solenoids is equal to half the number of engine cylinders. A review and analysis of the basic concept is given, and test results are discussed.

With the advent of electronic controls and development of electromagnetically controlled fuel injection pumps, the cost of fuel systems using plunger-type pumps was substantially reduced. Further reduction in cost can be achieved if fewer solenoid valves are used. A new type of injection pump combining electromagnetic spill control principle with distributor-type operation is described. Only one solenoid valve is required for a multi-cylinder engine. The pump was designed for port injection of gasoline, but with some modifications could be adapted to direct fuel injection. The fuel injection system includes a controller capable of electronic trimming of port-to-port fuel distribution for tight control of air to fuel ratios in all engine cylinders. A review of the basic concept and operating principles is given, and test results as well as cost considerations are discussed.

Two-stroke gasoline engines are known to benefit from using in-cylinder fuel injection which improves their ability to meet the strict fuel economy and exhaust emissions requirements. A conventional method of in-cylinder fuel injection involves application of plunger-type positive displacement pumps. Two-stroke engines are usually smaller and lighter than their 4-stroke counterparts of equal power and need a pump that should also be small and light and, preferably, simple in construction. Because a 2-stroke engine fires every crankshaft revolution, its fuel injection pump must run at crankshaft speed (twice the speed of a 4-stroke engine pump). An electronically controlled fuel injection system has been designed to satisfy the needs of a small automotive 2-stroke engine capable of running at speeds of up to 6000 rpm.